Embodiments of the present invention relate to a semiconductor memory device, and more particularly to a semiconductor memory device including a current driver that is capable of providing a linearly-changing drive current by minimizing influence caused by threshold voltage variation of a transistor, which may be generated according to a fabrication process or an operation temperature of the semiconductor memory device.
A current driver provides a current to a plurality of memory cells where data is stored in response to the current, and it may include a plurality of transistors. Threshold voltages of the transistors may change according to a fabrication process and/or temperature variation. The magnitude of a current flowing in one terminal, e.g., a drain, of each transistor may increase in proportion to the square of a threshold voltage.
If the transistor is driven at a specific voltage, a current flowing through the transistor may be changed according to a voltage change. The current change may affect the amplitude or a maintenance time of an output voltage or current of the transistor. Since the magnitude of a write current provided from the current driver is not stabilized by the threshold voltage deviation of transistors in the current driver, data distribution may substantially increase.
The increased data distribution may cause write failure, and thus repeated writing and verification operations are required. As a result, an operation time is unavoidably increased, which reduces the operation reliability.